In the art of audio sound reproduction it is well-known that the dynamic loudspeaker is more nonlinear and generates more distortion than all the other system components combined. This is particularly true at low frequencies which require large cone excursions where the stiffness of both the inner spider and the outer surround increases rapidly as the cone approaches its peak displacement, resulting in a nonlinear suspension compliance generating high distortion.
For example, in a typical high fidelity sound system at a frequency of about 40 Hz the total harmonic distortion of the amplifier might be of the order of 0.01%, whereas the distortion of the loudspeaker might range from about 4.0% to about 40.0%, depending upon the loudness. That is, the amplifier is almost perfectly linear with a distortion so low as to be almost unmeasureable, whereas the loudspeaker is extremely nonlinear with gross distortion quite evident to the ear. This vast difference is due in large part to the fact that the amplifier distortion is reduced by a large amount of negative feedback, whereas the conventional loudspeaker has no feedback whatever. A typical amount of feedback in an amplifier might be about 40 db which serves to reduce the nonlinear distortion by a factor of 100, or two orders of magnitude. It has long been recognized in the art that if negative feedback could be applied around the loudspeaker in an effective and economical manner then the present marginal fidelity of the loudspeaker might be greatly improved so as to approach the near perfect fidelity of the amplifier.